The present invention relates to dispersions of finely divided synthetic resins in plasticizers, so-called plastisols, which may contain pigments, fillers and further auxiliaries, such as dyestuffs, heat and light stabilizers, and other additives.
Plastisols are free-flowing or pasty compositions which gel on heating to elevated temperatures and form a solid, viscoelastic mass after cooling down.
For coating painted surfaces, for example primed car bodies, with plastisols, special organic bases are proposed as adhesion promoters. Polyamine compounds are proposed, for example in German Auslegeschrift No. 2,232,885, compounds from the class of the Schiff bases are proposed in German Offenlegungsschrift No. 2,512,366, and imidazoles are proposed in German Offenlegungsschrift No. 2,327,958.
To build the organic bases described in these patent applications, the most diverse reactions are described. According to German Offenlegungsschrift No. 2,512,366, suitable Schiff bases containing urea and urethane groups are obtained, for example, by reacting addition products of isophorone diisocyanate and trimethylolpropane with the condensation products of diethylenetriamine with methyl isobutyl ketone.
Plastisols are used in many and varied ways, for example for the manufacture of foils and shaped articles and for coatings as well as for the formation, on metals, of coatings which insulate against sound and protect against corrosion and flying stone chips, for example for air-conditioning ducts and metal doors. A further very important area of application is the use as a metal-bonding agent, for impregnating seams and as an undercoat on motor vehicles.
Most applications have in common that pasty compositions are processed to give relatively thick layers using methods known for the distribution of liquids, for example by means of whirler coating to prepare shaped articles, by means of knife-coating or spreading on fiber webs for the manufacture of synthetic leather, and by means of airless spraying to form undercoat layers on automobiles.
This type of processing presupposes a very pronounced non-Newtonian to thixotropic flow behavior of the plastisols, which effects that the plastisols can readily be spread under the shear stress of application but very rapidly develop a high viscosity in the stationary state after application.
Many methods have been tried to obtain this viscosity behavior, for example choice of fillers and of PVC according to particle size and shape, choice of plasticizers, addition of solvents and of viscosity-regulating additives, for example organically modified montmorillonites, finely divided amorphous silica prepared by flame hydrolysis, soaps of polyvalent metals, such as alumimun oleate or calcium ricinoleate, and the like.
Obtaining the non-Newtonian/thixotropic flow behavior desired is made particularly difficult by the presence of the organic-basic adhesion promoters proposed in the specifications listed above, since these adhesion promoters act as structure or thixotropy breakers.
Attempts have already been made in accordance with German Offenlegungsschrift No. 2,928,928, having a filing date of July 18, 1979, and a publication date of Jan. 29, 1981, to improve the flow behavior of plastisols by adding an isocyanate-free reaction product, of a polyamine compound with a polyisocyanate.